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T. G. MARTIN. TWO-WIRE PARTY LINE 'LocKqqT TELEPHONE SYSTEM,

' APPLICATION FILED DEC 5,1919 I Reissued Apr. 20, 1920.

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I T. G. MARTIN. TWO-WIRE PARTY LINE LOCKOUT TELEPHONE SYSTEM.

APPLICATION FILED DEC- 5.1919.

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Reissned Apr. 20, 1920.-

T. G. MARTIN.

TWO-WIRE PARTY LINE LOCKOUT TELEPHONE SYSTEM.

I APPLICATION FILED DEC- 5, 1919- Relssued Apr. 20, 1920. 14,846;

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UNITED STATES rATEN OFFICE.

TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TWO-WIRE PARTY-LIN E LOCKOUT TELEPHONE SYSTEM.

. Specification of Reissued Letters Patent. Reissued Apr, 20, 1920,

Original No. 1,291,587, dated January 14, 1919, Serial No. 600,610, filed January 3, 1911. Renewed April 29, 1918, Serial No. 231,539. Application for reissue filed December 5, 1919. Serial No. 342,826.

To all whom it may concern Be it known that I, TALBOT (3r. MARTIN, a citizen of the United States of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in TwoWVire Party-Line Lookout Telephone Systems, of which the following is a specification.

My invention relates to telephone systems in general, but more particularly to lockout party 'line systems, and especially to those having provisions for calling automatically or semi-automatically.

My invention relates to party-line systems, for example, in. which the look-out means are controlled by the normal condition of the line to enable the calling subscriber .to take the line, and in which this normal condition of the line is changed as soon as the line is taken, in order that some other subscriber on the same line may not interfere with said first subscriber in the use thereof.

Generally stated, therefore, the object of my invention is to provide improved means for enabling a line when once taken to be retained by the subscriber so taking it, and to enable him also, if he so desires, to send impulses over said line for operating automatic switches or signals.

It is also an object to provide certain details and features of improvement and combinations tending to increase the efficiency and serviceability of a telephone exchangev system of this particular character.

To the foregoing and other useful ends my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings Figures 1 and 2 taken together show a complete circuit connection between a calling substation A (Fig. 1), and a called substantion A (Fig. 2) in a system embodying the principles of my invention. I

Fig. 3 is a diagrammatic representation .of the essential features of the so-called master switch D (Fig. 1).

In Fig. 1 there is shown a party-line to which the two telephones A and A are connected. This line is connected with the individual or line switch C at the central ofiice.

A number of individual switches C are controlled by a common master switch I) and have common access to a group of trunk lines each of which leads to a selector similar to selector E. The selector E, together with a number of other similar switches, has common access to a number of groups of trunk lines leading to connector switches F (Fig. 2), which in turn have direct access to the calling terminals of the subscribers lines.

The line switches C and C and master switch D are of the general type disclosed in British Patent No. 26,301 of 1906, and in the American Telephone Journal, of New York, N. Y., of June 6, 1908, having a somewhat modified construction. Referring to the line switch C, the operating winding 2,

cut-off winding 3, and line winding 4, and

auxiliary Winding 11, are placed upon a single core forming a plural wound electromagnet having twodistinct magnetic circuits, so that the windings upon one end have no effect upon the armatures upon the other end. Of the windings upon the upper end of the magnet the winding 2 is strong enough to operate both the plunger arm 12 and cut-off armature 5, while the winding 3, though strong enough to operate the armature 5 and to hold the plunger arm 12 in its operated position, is not strong enough to attract said plunger arm from its normal position.

The selector E is of the general type-disclosed in United States Letters Patent No. 815,321, issued March 13, 1906, to Keith, Erickson and Erickson, 'being modified somewhat, however, in order to operate in a two-wire system, i. e., a system. in which the central office apparatus is controlled by impulses transmitted from the calling substation over the two sides of the line in series. The release magnet 105 is preferably arranged to release the switch mechanism immediately upon energizing in the manner shown in United States Letters Patent No. 815,176, for connector switches, rather than upon definergiziug as shown in said selector patent No. 815,321. The relays 144:, 51 and '38 deenergize slowly when their energizing circuits are broken.

The connector F is of the general type disclosed in United States Letters Patent No 815,176, issued March 13, 1906, to Keith,

tor, is'modified tooperate in a two-wire system.

The substations may be of any suitable common battery two-wire automatic type. The ones with which I have elected to illustrate my invention comprise the usual receiver 6 (see substation A, Fig. 1), switch hook 7, transmitter 3 and ringer 9. For the purpose of producing impulses for controlling the central oflice apparatus, this substation is also provided with a pair of pulse springs 10 and 11, impulse wheel 18 and a'dial (not shown). A pair of springs 8 and 9 are provided for closing ashunt circuit about the transmitter and receiver. In the preferredform of my inventionI provide each substation with a relay which is adapted, when in an operated position,- to close'the contact between the springs 14- and 15, thereby bridging the talking circuit across the line conductors. The relay is, also provided with a spring 19, which, when the relay is energized, catches and locks the 'armature 20 in its operated position until the receiver hook is pulled down. Since the relay, when energized, is locked up mechanically it cannot be affected by any change in the circuit conditions of the tele-v phone,-such as the opening of the line for the purpose oftransmitting impulses to the.

central ofiice. One terminal of the winding of the relay 13 is connected to the conductor 16, while the other terminal is connected to the hook switch spring 21, which normally engages the spring 22. As the switch hook rises when the receiver is removed, the spring 23 which is connected to the line conductor 17 engages the spring 22 and forces it out of engagement with the spring 21. Thus, for an instant during the upward movement of the switch hook all these springs 21, 22 and 23 are in contact, thereby momentarily bridging the relay 13 across the line. The relay 13 is so wound and adjusted that when it is thus bridged across the line it receives sufiicient current from the central office to be operatively energized. If, however, the talking circuit of some other telephone is in bridge'of the line at the time the circuit of the relay 13 is closed,

sufiicient current is shunted away from the relay by said talking circuit to prevent the relay from being operated. It will be understood that the relay 13 may have any suitable resistance, so as to secure its proper operation. Since the bridging of the talking circuit at a telephone across the line is dependent upon the operation of the relay 13 atthat telephone, it will be seen that it will be impossible for a second subscriber to come in on the line while some other subscriber is' using it. In case one, subscriber wishes to call another subscriber on the same line, the first subscriber can, by pressing the button 25 and removing the shortcircuit fromthe resistance 26, increase the resistance of his talking circuit sufficiently at the time the second subscriber removes second telephone in talking condition.

In order to notify a calling subscriber whether or not the line is busy when he attempts to make a call, I provide an opening in the wall of the telephone. Upon the end;

of the arm 28 of the receiver hook there is placed a 'small target or signal, which may have the word busy written on it. When the receiverhook rises this target comes be-' hind the opening 27 and may be seen by the subscriber. T0 the armature 20 there is at- ,tached an arm 29 carrying a shield 30 which, when the relay is energized, comes behind the opening 27 ,but in front of the target on the switch hook arm 28, thereby hiding said target from the calling subscriber. v.

The operations by which one subscriber calls another in the system shownv herein are as follows: It will be assumed, first that the subscriber at substation A calls subscriber A No. 220. When thesubscriber at substation A removes his receiver a moment- 23, 22 and 21, relay 13, line 16, springs 34 and 33 and winding4 to the battery lead 35, thence to battery B and to ground; The relay 13 is energized by this impulse and locks up, bridging the talking circuit acrossthe line. The winding 4 of the switch C,

upon energizing, attracts the armature 36,"

which closes the circuitvof the winding 2. This circuit 1 extends from ground G through the springs 31 and 110, windings 2 and 111, contact point 112 and armature 132 to the battery lead 35. The winding 2, upon energizing, attracts-the plunger arm 12 and cut-'ofl armature 5'. The plunger arm 12, upon being attracted, operates to force the line switch plunger into a bank of contact'springs 113, 114, 45, 44, 115, 116, 117 and 118, forcing them into contact in pairs as shown in the drawings. The armature 5, upon operating, disconnects the line winding 4 and ground G from the calling line, whereupon the armature 36 falls back and opens the circuit of the winding 2. Be fore the winding-2 is deenergized', however, a circuit is closed through the winding 3 in the following manner: When the springs 113 and 117 are forced into contact with'the springs 114 and 118 by the plunger of the station A,line 16, springs 113 and 114, side switch wiper 120 and the u per winding of the relay 37 to battery. he line relay 37 of the Selector thereupon i energizes and closes the circuit of the slow acting relay 38. This relay 38, upon energizing, com.- pletes a circuit from ground Gr through the springs 40, 41, 42, 43, 44 and 45 and wind-.

ing 3 of the switch C to battery. The wind.- ing 3 holds the switch C in its operated position after the armature 36 has fallen back and broken the circuit of the winding 2. In order to insure against the armature 36 falling back before the winding 3 is energized,

the auxiliary winding 111 is energized in series with the pull-down winding 2 and is short-circuited through the-springs 121 and 122 when the plunger arm reachesthe limit of its downward movement. The winding 111 thus serves to hold up the armature 36 for an instant after the winding 4 is de'ner gized, so as to give the winding 3 a little longer time in which to energize. When the line switch Q operates, the master switch D operates in a well-known manner to advance the plungers of the idle line switches to an idle trunk.

. of a trunk line.

The operation of the'master switch Dis as follows: The closure of contact between the springs 115 and 116 of the line switch 0 completes a circut from ground G through the springs 115 and 116, contact point 123 (which is assumed to correspond to'the trunk seized by the switch C), wiper 124, segment 165 and relay 125 to battery. The relay 125, upon energizing, closes a circuit through the relay 126; The relay 126, upon energizaing, withdraws the pin 127 from an opening in the locking plate 128, and closes a circuit through the motor'magnet 129. This circuit extends from ground G through the magnet 129, interrupter springs 130, contact point 131 and armature 132 to battery. The magnet 129 operates in a manner similar to that of a buzzer as long as the armature 132 engages the contact point 131, and, through breaks the circuit of the relay 126. They master switch continues to operate, however,

until the next opening in the plate 128 passes directly under the pin 127, whereupon the armature 132 falls back and breaks the circuit of the magnet 129. The openings in the plate are so spaced that the armature 132 can fall back only when the plungers of the line switches are directly in front If busy trunk lines have to be passed before the plungers can arrive at an idle trunk, the relays 125' and 126 are calling device for the first digit 2 of the number desired,- whereby the impulse springs 10 and 11 which are included in the bridge at thev substation are separated twicev momentarily, each time opening the line or inserting a high resistance therein and thereby causing the line relay 37 of the selector E to be denergized. In order to eliminate the resistance of the transmitter and re-' ceiver from the line circuit, the short-circuit through the springs 8 and 9 is closed at this time. This short-circuit can be closed in any desired manner, but is preferably placed under'the control of the calling device, so that when the calling device is operated, the springs 8 and 9 are brought into contact to'close this short-circuit. The

relay 37, upon denergizing, closes a circuit from ground G through the springs 46, 48, 49'and 50 (the slow-acting .relay 38' does not fall during the momentary interruption of its circuit), relay 51, vertical'magnet 52 and side switch wiper 53. to battery. The vertical magnet operates to raise the switch shaft two steps, while the ,slow-acting' relay 51 operates to close the circuit of the private magnet 54. The relay 51, does not have time to denergize until after the last impulse for the digit is delivered, when it breaks "the circuit of the magnet 54, which denergizes and 'allows the side switch to pass to second position- The rotary magnet 55 thereupon operates in a well-known manner to rotate the wipers onto an idle position, cutting off the line relay of theselector and extending the line'to the line relays 56 and 57 of the connector, whereupon said relays become energized. The energizing circuit for these relays extends from ground G through the relay 57, trunk conductor 137, thence'over the heavy conductors through ,the selector E, line switch C, substation A and back over the other side of the line through the switches C and E, trunk conductor 13.8 and relay 56 to battery. The relay 57 of the connector, upon energizing, completes a circuit from ground G through the springs 58 and 59, 60 and 61 and relay 62 to battery. The relay 62, upon energizing, extends a connection. from ground G through the side switch wiper 63 and springs 64 and 65 to the conductor- 66, for the purpose of-providing a guarding potential for the selector private bank contacts of the seized trunk, and for maintaining a holding circuit for the relay 38 of the selector E. This holding circuit extends from ground G through the side switch wiper 63, springs 64 andJ65, conductor 66, private bank contact and wiper 140, side switch .wiper'141, springs 143 and 142 and relay 38 to battery. The relay 144 of the selector E is energized in series with the rotary magnet, and, being slow acting, remains in its operated position for an instant after the side switch passes is again opened twice, each time breaking:

the circuit of the relays 56 and 57 at the C011. nector. The slow relay 62 does not have time to fall back durin the momentary interruption of its circuit by the relay 57; consequently, each time the relay 56 .den'ergizes, a circuit is closed from ground Gr through the springs 67, 68, 69 and 70, relay 71, vertical magnet 72 and side switch wiper 73 to battery. The magnet 72 operates to raise the shaft and wipers two steps, while the slow acting relay 71 acts in the same manner as explained for the relay 51 of the selector E to cause the private magnet 74 to trip the side switch to second position. In passing from first to second position, the

side switch wiper 73 transfers the battery connection from the vertical magnet to the rotary magnet 75. When the calling device is operated for the last digit 0 the rotary magnet receives ten impulses and rotates the wipers ten steps onto the contacts of the line #220, after which the side switch is tripped to third position by the private magnet in the same manner in which it was tripped to second position after the completion of the impulses for the first digit. The operating circuit of the rotary magnet 75 extends from ground G through the springs 67 and 68, 69 and 70, relay 71, springs 146 and 147, magnet 75 and side switch wiper 73 to battery. When, the .side switch reaches third position the connection between the I calling and the called lines is completed, the

called line is provided with a guarding potential at the connector private bank con-' tacts, the line-winding of the line switch C is cut off and a circuit is closed through the ringing rela 76'. .The switch C is cut off by the windin 77, which is energized over a circuit e'xten ing from ground (1 through the sideswitch wiper 78, private wiper 79 and winding 77 to battery. The energizing circuit of the relay 76 extends from ground Gfiigf through the interrupter 80, "springs 81 and '82, relay 76 and the side switch wiper 73 to battery. The relay 76 is energized in- Of course, the relay 144, deenertermittently to. ring the called subscriber. The ringingcircuit extends from one term1nal of the ringing current generator N through the springs 148 and 149, side switch wiper 150, shaft wiper 151, line 152, substation springs 153' and 154, ringer-and condenser -155, line 156, springs 157 and 158, wiper 15 9 and springs 160 and 161 to the other terminal of the generator. Vhen the receiver at the called substation is removed that substation is provided with talking current through the back-bridge relay 83 of the connector. This circuit overwhich the talking current is supplied extends from ground G through the side switch wiper 78, lower winding of the relay 83, ringing relay springs 162 and 149, side switch wiper 150, line wiperv 151, thence over the heavy conductors to and through the substation A and back over the other side of the line, and through the ringing relay springs 160 and 163, springs 164 and 165, upper winding of the relay 83 and side switch wiper 73 to battery. The relay 83, upon energizing, closes a circuit from ground G through the springs 67 and 84 of the relay 56,springs 85 and 86, relay 87 and side switch wiper 73 to battery. The relay 87, upon energizing, breaks the operating circuit of the relay 76 and closes a locking circuit for itself through the springs 88.

The two connected subscribers may now carry on an uninterrupted conversation, and no other subscriber on either line can break .in on the connection. Referring to Fig. 1,

suppose the receiver at substation A is removed. As the hook goes up a circuit will be closed through the rela-y'13 at that sta-. tion, but said relay will be shunted-- by the talking circuit at the substation A and will not be operated, thereby leaving the talkin circuit open, as shown in Fig. 1.

In case'the called line has been busy when the connector F sought to make connection therewith, the private wiper 79 would have found its private contact grounded and immediately uponengaging said contact would have extended a ground potential through the side switch wiper 7 8 (in second position), springs 90 and 89 and lower winding of the relay 91 to the spring 92 of the private magnet relay 71 and through the private magnet 74 to battery. As the relay 71 denergizes after the last digit was called, the private magnet would have been maintained energized over the above circuit by the ground at, the private wiper, locking the side switch in second position, and at the same time the relay 91 would have been energized. This relay, upon energizing,

tion, no connection would be completed with the bus line, and the busy signaling machine Ni would be connected with the calling line by the closure of the springs 95 at the relay 91.

From the foregoing it is evident that the connector cannot make connections with a line which has a groundupon its connector private bank contacts. It will also be seen that as soon as the connection isextended to the selector E a guarding potential is extended from ground G through springs 40, 41, 42, 43, 44 and 45, ductor 96 to the connector private bank contacts of the calling line. In order to permit a subscriber to call on his own line to signal another subscriber thereon, each trunk line leading to a selector E is provided with the relays 97 and 98, which 'so modify the guarding potential of the calling line while the calling device at the calling station is being operated as to allow a connector to make'connection therewith at that time. It will be seen that all impulses must pass through the relay 97 which, upon deenergizirliag after connection is extended to the selector closes a circuit through the slowacting relay 98. The relay 98, upon energizing, removes the short-circuit around the I resistance 99, thereby inserting this resistance in the groundconnectlon to the private contacts of the calling line. Thus it will be seen that when the calling subscriber is calling back on his own line, at the time the private magnet relay 71 deenergized after the last digit is called, the resistance 99 will be included in the circuit, which tends to lock the private magnet. The resistance is high enough to prevent said magnet from being locked, and the side switch passes to third. position in the usual manner. A moment later the relay 98 '(Fig. 1) falls back and cutsout the resistance 99 to' restore the guarding potential of the calling line to its effective condition.

When a calling subscriber calls back on his own line a circuit .will be closed through the back-bridge relay of the connector and the calling substation, which will cause the circuit of the ringer relay 76 to be opened. In order to signal the called substation the calling subscriber must press the button 25, thereby increasing the resistance of the bridge sufiiciently to allow the connector line relay 56 to fall back, but not the relay 57. The relay 56, upon falling back, breaks the circuit of-the relay 87, which falls back and closes the circuit ofv the ringer relay. The pressing of the button 25 also increases the resistance of the bridge at substation A sufiiciently to allow the relay 13 at the called substation to be energized when the called subscriber answers. The bridging of the called telephone across the line causes the relay 56 to again pull up, which causes the allows the connector line and over the con-- ringing current-to be cut subscriber then releases his After a connection is completed the switches are released by the hanging up of the' receiver at the calling substation. This off. The calling button.

which removes the holding ground from the release relays 62 and 38 of theswitches F and E, respectively. The relay 62, upon deenergizing, completes the circuit of the release magnet 101, which releases the connector. The circuit of the magnet 101 is broken at the springs 102 and 103 when the switch shaft reaches its lowest position. In like manner the selector E is released by the magnet 105 when the relay 38 falls back. When the relay 38 denergizes it also breaks the holding circuit of the wind 'ing 3 of the switch C, allowing its plunger to be restored.

In party-line systems of the kind shown herein, the different parties on a line may be signaled selectively known manner: The bells of the difl'erent substations may adapted to respond'to only a certain kind of ringing current. Each subscribers line may be accessible by a plurality of groups of connectors, each group representing a different hundred digit. The numbers of the difl'erent substations on the same line may then be given different hundred digits,

in the following well be tuned or otherwise relays to fall back,

corresponding to the respective hundreds.

of groups of connectors. Each group of connectors may be supplied with ringing current. of the proper character to operate only the ringers of the substations whose hundreds digits correspond to that connector group. Thus, tosignalany particular substation on a line the line must be called through a connector in a group, which the switch hook. A line is spoken of as being in normal position when the receivers of all telephones on switch hooks.

What I claim as my invention is: p

1. In a telephone system,a party-line havg a plurality of telephone stations thereon,

normal po-' sltion, 1t 1s meant, that the rece ver is on said line are on their a relay at each of said stations, means for only momentarily energizing said relay when said line is taken for use at any station, means outside the central station controlled by said relay for-preventing any other subscriber from coming in on said line when said line is busy, a calling device for said party line, and a progressively movable switch associated with said line, said venting 'said line, said eration of the calling device for extend ng switch responsive to the oper ation of the calling device for extending connection to the'called line.

2. In a telephone system, a party-line having a plurality of substations thereon, a relay-at each of said substat ons, means for only momentarily energiz ng the corresponding relay when a receiyer is removed from the hook at a substation, means for locking said relay in energized position, means outside the central station controlled by the energization of said relay for preany other subscriber from comlng in on said line while the same is in use, a calling device for said party lines, and a progressively movable switch associated with said line, said switch responsive to the operation of the calling device for extending connection to the called line.

3. In a telephone system, a party-line having a plurality of subscribers stations thereon, a relay bridged across the line at each of said stations, means for only 'momentarily energizing one of said relays upon the removal of the corresponding recelver from its hook, means controlled by said relay tor closing the talking circuit, means outs1de the central station for preventing said relay from energizing when a receiver is removed from the hook and said line is busy, a call ing device for said party line, and a progressively movable switch assoclated with switch responsive to the opconnection to the called line. 4

4. In a telephone system, a party-line having a plurality of substations thereon, a relay at each substation bridged across said line, means for only momentarily energizing one of said relays upon removing a receiver from its hook, means for locking said relay in energized position, means outside the central station operated by said relay for closing a low resistance talking bridge across said line in shunt of said relay, said shunt preventing any other relay being en ergized upon the removal of any other subscribers receiver from the hook, a calling device for said party line, and a progres sively movable switch associated with said line, said switch responsive to the operation of the calling device for extending connection to the called line.

5. In a telephone system, a party line having a plurality of substations thereon, an

automatic trunking switch for said line, a

relay at each substation bridged across said line, means for only momentarily energiz ing one of said relays upon removing a receiver from its hook, said automatic switch also responsive to the raising of the switch hook to perform a trunking operation, means for locking said relay in energized position, means operated by said relay for closing a low resistance bridge across said line in shunt of said relay, said shunt preventing any other relay being energized preventing the release of the automatic switch while the shunt is so affected.

6. In an automatic telephone system, a line extending to a central exchange, automatic switches at the exchange, stations on said line, a low resistance bridge at each station including a device for interrupting the same to operate said switches, said bridges normally disconnected from across the line, a high resistance magnet at each station for closing the associated bridge, aswitch at each station operable to connect the magnet thereat momentarily across the line circuit, and means for operating the switch at any station when the receiver is removed.

7. In an automatic telephone system, a line extending to a central exchange, automatic switches at the exchange, stations on said line, a bridge at each station including a device for interrupting the same to operate said switches, said bridges normally disconnected from across the lines, a magnet at each station for closing the associated bridge, and means operated upon the initiation of a call at any station for momentarily connecting the magnet at that station across the line, whereby the same may be operated to close the associated bridge, said bridges and said magnets being of such relative resistances that whenever one of said bridges is closed a magnet subsequently connected across the line will not be energlzed.

8. In an automatic telephone system, a line extending -to a central exchange, automatic switches at the exchange, stations on said line, a bridge at each station including a device for interrupting the same to operate said switches, said bridges normally disconnected from across the line, a magnet at each station for closing the associated bridge, means operated upon the initiation of a call at any station for momentarily connecting the magnet at that station across the line, whereby the same may be operated to close the associated bridge, said bridges and said magnets being of such relative resistance that whenever one of said bridges is closed a magnet subsequently connected across the line will not be energized, means for locking each magnet in operated position, and unlocking means at each station actuated upon the replacement of the receiver.

9. In a telephone system, a line extendin to a central exchange, a battery bridged across said line at the exchange, a station on any oneof said calling nections from said switch whereby in its normal position the said signaling bridge is closed, whereby in its intermediate position the said magnet is connected across the line, and whereby in its final position the said magnet is, again disconnected, and a receiver hook for controlling said switch.

. 10. In an automatic telephone system, a first line, a second line, means for connecting said lines to establish a talking'circuit between the two, said means including an automatic switch havin a progressively movable element through which closed as a result of the progressive action of the switch, said first line having two conductors, said conductors included in the talking circuit in series, a plurality of telephones associated with said first line, each telephone having an autom tic impulse sending device and means for br dging the telephoning apparatus across the line for talking between the first and second lines, said automatic switch responsive to impulses produced by devices over a circuit including the-two sides of the said first line in series, the means for bridging the telephoning apparatus of any station across the line controlled by the telephoning apparatus of any other station when said tele- \phone apparatus is thrown across the line, to

render the said means ineffective for con necting a telephoning apparatus across the line.

11, In a telephone system, a line includthe talking circuit ising a pair of talking conductors, an autoinatic switch controlled over a circuit including said talking conductors in series, a plurality of telephones for said line, an impulse sender for each telephone for operating said switch, an eletromagnetic lock-out device for each telephone, and a circuit for each lockout device controlled by the switch and the telephone.

12. In a telephone system, a line including a pair of talking conductors, an automatic progressively movable switch, a plurality of telephones for said line, an im pulse sender for each telephone for controlling said switch over the said line conductors in series, an electromagnetic lock-out mechanism for each telephone and a common battery for supplying talking current to the telephones on said line.

13. In a telephone system, a party line including a pair of talking conductors, a common battery for talking purposes, automatic means controlled by a calling subscriber over a circuit including the said talking conductors in series toestablish communication with the called subscriber, and automatic means for preventing the subscribers on the said line interfering with an established con nection, both of said means operated by current from said battery. 4

Signed at Chicago, Cook county, this 2nd day of December, 1919.

TALBOT e. MARTIN.

Illinois, 

